U.S. patent application number 12/719367 was filed with the patent office on 2011-09-08 for method for collection and communication of measured data within a fuel cell stack.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS, INC.. Invention is credited to Kenneth L. Kaye, David D. Rea, Michael F. Zawisa.
Application Number | 20110217613 12/719367 |
Document ID | / |
Family ID | 44531637 |
Filed Date | 2011-09-08 |
United States Patent
Application |
20110217613 |
Kind Code |
A1 |
Rea; David D. ; et
al. |
September 8, 2011 |
METHOD FOR COLLECTION AND COMMUNICATION OF MEASURED DATA WITHIN A
FUEL CELL STACK
Abstract
A system for communicating measurement data from each fuel cell
or a group of fuel cells in a fuel cell stack, including a
plurality of fuel cells and a plurality of stack plates, where one
stack plate is between each fuel cell and on each end of the stack.
The system includes a plurality of embedded smart plates where each
embedded smart plate is mechanically and electrically coupled to at
least one of the plurality of stack plates, and where each embedded
smart plate includes optical transceivers on a top side and a
bottom side of the smart plate. The system further includes at
least one aggregator device having at least one optical transceiver
to initiate a series of communications between the embedded smart
plates to determine the location and data collected by each of the
smart plates.
Inventors: |
Rea; David D.; (Pittsford,
NY) ; Zawisa; Michael F.; (Victor, NY) ; Kaye;
Kenneth L.; (Fairport, NY) |
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS,
INC.
DETROIT
MI
|
Family ID: |
44531637 |
Appl. No.: |
12/719367 |
Filed: |
March 8, 2010 |
Current U.S.
Class: |
429/432 ;
429/428 |
Current CPC
Class: |
Y02E 60/50 20130101;
H01M 8/04 20130101 |
Class at
Publication: |
429/432 ;
429/428 |
International
Class: |
H01M 8/04 20060101
H01M008/04 |
Claims
1. A system for communicating measurement data from fuel cells in a
fuel cell stack, said system comprising: a plurality of fuel cells,
each fuel cell generating a voltage potential; a plurality of stack
plates, including one stack plate between each fuel cell and on
each end of the fuel cell stack to collect the voltage potential
generated by the fuel cells; a plurality of embedded smart plates,
each embedded smart plate being mechanically and electrically
coupled to at least one of the plurality of stack plates in the
fuel cell stack, each embedded smart plate including optical
transceivers on a top side and a bottom side of the smart plates,
each of the embedded smart plates receiving operating power from
the fuel cell stack via the voltage potential from the fuel cell
adjacent to the stack plate that the embedded smart plate is
coupled to; and at least one aggregator device, said at least one
aggregator device including at least one optical transceiver for
initiating communication with the embedded smart plate adjacent to
the at least one aggregator device, wherein the aggregator device
initiates communication with the embedded smart plate to initiate a
series of communications between the embedded smart plates in the
stack to determine the location and the measurement data collected
by each of the embedded smart plates in the stack.
2. The system according to claim 1 wherein each of the optical
transceivers on each of the embedded smart plates and on the at
least one aggregator device includes an optical transmitter and an
optical receiver.
3. The system according to claim 2 wherein the optical
transceiver(s) on each of the embedded smart plates and on the at
least one aggregator device are aligned with the optical receivers
on adjacent embedded smart plates and/or the aggregator device.
4. The system according to claim 1 wherein each of the embedded
smart plates further includes additional optical transceivers for
by-passing an embedded smart plate that is not functioning
properly.
5. The system according to claim 1 wherein the optical transceivers
of each embedded smart plate have different spectral emissions and
responses.
6. The system according to claim 1 wherein the location, the
measured cell voltage and/or high frequency resistance of each fuel
cell in the stack is communicated by the embedded smart plates to
the aggregator device.
7. The system according to claim 1 wherein each embedded smart
plate includes an embedded smart plate printed circuit board having
a low-input voltage DC-to-DC converter, an analog-to-digital
converter, a microprocessor and a voltage reference.
8. A system for communicating measurement data from fuel cells in a
fuel cell stack, said system comprising: a plurality of fuel cells;
a plurality of stack plates, including one stack plate between each
fuel cell and on each end of the stack; a plurality of embedded
smart plates, each embedded smart plate being mechanically and
electrically coupled to at least one of the plurality of stack
plates in the fuel cell stack, and each embedded smart plate
including an embedded smart plate printed circuit board and optical
transceivers on a top side and a bottom side of the smart plates;
at least one aggregator device, said at least one aggregator device
including at least one optical transceiver for initiating
communication with the embedded smart plate adjacent to the at
least one aggregator device; and a controller that is configured to
control the aggregator device, wherein the controller requests that
the aggregator device communicate with the embedded smart plate
adjacent to the at least one aggregator device to initiate a series
of communications between the embedded smart plates in the stack to
determine the location and measurement data collected by each of
the smart plates in the stack.
9. The system according to claim 8 wherein each of the optical
transceiver(s) on each of the embedded smart plates and on the at
least one aggregator device includes an optical transmitter and an
optical receiver.
10. The system according to claim 9 wherein the optical
transceivers on each of the embedded smart plates are aligned with
the optical receivers on adjacent embedded smart plates and/or the
aggregator device.
11. The system according to claim 8 wherein the embedded smart
plates are embedded in the fuel cell stack in a columnar
arrangement.
12. The system according to claim 8 wherein the optical
transceivers on each of the embedded smart plates have different
spectral emissions and responses.
13. The system according to claim 8 wherein the location and
measurement values such as cell voltage, high frequency resistance
and/or temperature of each fuel cell in the stack is communicated
by the embedded smart plates to the aggregator device via the
optical transceivers.
14. The system according to claim 8 wherein each embedded smart
plate printed circuit board includes a low-input voltage DC-to-DC
converter, an analog-to-digital converter, a microprocessor and a
voltage reference.
15. The system according to claim 8 wherein the aggregator device
receives its operating power from a battery.
16. A system for communicating measurement data from fuel cells in
a fuel cell stack, said system comprising: a plurality of fuel
cells; a plurality of stack plates, including one stack plate
between each fuel cell and on each end of the fuel cell stack; a
plurality of embedded smart plates, each embedded smart plate being
mechanically and electrically coupled to a plurality of stack
plates in the fuel cell stack by at least one connector, each
embedded smart plate including optical transceivers on a top side
and a bottom side of each of the embedded smart plates; and at
least one aggregator device, said at least one aggregator device
including at least one optical transceiver for initiating
communication with the embedded smart plate, thereby initiating a
series of communications between the embedded smart plates and the
at least one aggregator device to determine the location and
measurement data collected by each of the embedded smart plates in
the stack.
17. The system according to claim 16 wherein each of the optical
transceivers on each embedded smart plate and on the at least one
aggregator device includes an optical transmitter and an optical
receiver.
18. The system according to claim 16 wherein the optical
transceivers on each of the embedded smart plates are aligned with
the optical receivers on adjacent embedded smart plates and/or the
adjacent aggregator device.
19. The system according to claim 16 wherein the location and
measurement values such as cell voltage, high frequency resistance
and/or temperature of each fuel cell in the stack is communicated
by the embedded smart plates to the aggregator device via the
optical transceivers.
20. The system according to claim 16 wherein each embedded smart
plate includes an embedded smart plate printed circuit board having
a low-input voltage DC-to-DC converter, an analog-to-digital
converter, a microprocessor and a voltage reference.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates generally to a fuel cell stack
monitoring system and, more particularly, to a monitoring system
for a fuel cell stack that employs an aggregator device for
collecting optical signals indicative of measured parameters of
each fuel cell or group of fuel cells in the stack.
[0003] 2. Discussion of the Related Art
[0004] Hydrogen is a very attractive fuel because it is clean and
can be used to efficiently produce electricity in a fuel cell. A
hydrogen fuel cell is an electro-chemical device that includes an
anode and a cathode with an electrolyte therebetween. The anode
receives hydrogen gas and the cathode receives oxygen or air. The
hydrogen gas is dissociated in the anode side catalyst to generate
free protons and electrons. The protons pass through the
electrolyte to the cathode. The protons react with the oxygen and
the electrons in the cathode side catalyst to generate water. The
electrons from the anode cannot pass through the electrolyte, and
thus are directed through a load to perform work before being sent
to the cathode.
[0005] Proton exchange membrane fuel cells (PEMFC) are a popular
fuel cell for vehicles. The PEMFC generally includes a solid
polymer electrolyte proton conducting membrane, such as a
perfluorosulfonic acid membrane. The anode and cathode electrodes
(catalyst layers) typically include finely divided catalytic
particles, usually platinum (Pt), supported on carbon particles and
mixed with an ionomer. The catalytic mixture is deposited on
opposing sides of the membrane. The combination of the anode
catalytic mixture, the cathode catalytic mixture and the membrane
define a membrane electrode assembly (MEA). Each MEA is usually
sandwiched between two sheets of porous material, a gas diffusion
layer (GDL), that protects the mechanical integrity of the membrane
and helps in uniform reactant and humidity distribution. The part
of the MEA that separates the anode and cathode flows is called the
active area, and only in this area the water vapors can be freely
exchanged between the anode and cathode. MEAs are relatively
expensive to manufacture and require certain humidification
conditions for effective operation.
[0006] Several fuel cells are typically combined in a fuel cell
stack to generate the desired power. For example, a typical fuel
cell stack for a vehicle may have two hundred or more stacked fuel
cells. The fuel cell stack receives a cathode input reactant gas,
typically a flow of air forced through the stack by a compressor.
Not all of the oxygen is consumed by the stack and some of the air
is output as a cathode exhaust gas that may include water as a
reaction by-product. The fuel cell stack also receives an anode
hydrogen reactant gas that flows into the anode side of the stack.
The stack also includes flow channels through which a cooling fluid
flows.
[0007] A fuel cell stack includes a series of bipolar plates
(separators) positioned between the several MEAs in the stack,
where the bipolar plates and the MEAs are positioned between the
two end plates. The bipolar plates include anode side and cathode
side flow distributors (flow fields) for adjacent fuel cells in the
stack. Anode gas flow channels are provided on the anode side of
the bipolar plates that allow the anode reactant gas to flow to the
respective MEA. Cathode gas flow channels are provided on the
cathode side of the bipolar plates that allow the cathode reactant
gas to flow to the respective MEA. One end plate includes anode gas
flow channels, and the other end plate includes cathode gas flow
channels. The bipolar plates and end plates are made of a
conductive material, such as stainless steel or a conductive
composite. After stacking, these components are typically placed
under compression to minimize electrical contact resistances and to
close the seals. The end plates conduct the electricity generated
by the fuel cells out of the stack. The bipolar plates also include
flow channels through which a cooling fluid flows.
[0008] High frequency resistance (HFR) is a well-known property of
fuel cells, and is closely related to the ohmic resistance, or
membrane protonic resistance, of fuel cell membranes. Ohmic
resistance is itself a function of the degree of fuel cell membrane
humidification. Therefore, by measuring the HFR of the fuel cell
membranes of a fuel cell stack within a specific band of excitation
current frequencies, the degree of humidification of the fuel cell
membrane may be determined. This HFR measurement allows for an
independent measurement of the fuel cell membrane humidification,
thereby eliminating the need for RH sensors.
[0009] Typically, the voltage output and possibly the high
frequency resistance (HFR) of every fuel cell in the fuel cell
stack is monitored so that the system knows if a fuel cell voltage
or a fuel cell HFR is outside of a desired range, indicating a
possible failure. As is understood in the art, because all of the
fuel cells are electrically coupled in series, if one fuel cell in
the stack fails, then the entire stack will fail. Certain remedial
actions can be taken for a failing fuel cell, as a temporary
solution, until the fuel cell vehicle can be serviced. Such
remedial actions include increasing the flow of hydrogen and/or
increasing the cathode stoichiometry.
[0010] The fuel cell voltages and the HFR of the fuel cells are
typically measured by monitoring sub-systems that include a wire
connected to each bipolar plate in the stack and end plates of the
stack. Therefore, a 400 cell stack will include 401 wires connected
to the stack. Because of the size of the parts, the tolerances of
the parts, the number of the parts, etc., it may be impractical to
provide a physical connection to every bipolar plate in a stack
with this many fuel cells. Therefore, there is a need in the art
for a system and method for measuring cell voltage and HFR without
requiring wires connected to each bipolar plate.
SUMMARY OF THE INVENTION
[0011] In accordance with the teachings of the present invention, a
system for communicating measurement data from each fuel cell or a
group of fuel cells in a fuel cell stack is disclosed. The stack
includes a plurality of stack plates, where one stack plate is
between each fuel cell and on each end of the stack. The system
includes a plurality of embedded smart plates where each embedded
smart plate is mechanically and electrically coupled to at least
one of the plurality of stack plates, and where each embedded smart
plate includes optical transceivers on a top side and a bottom side
of the smart plate. The system further includes at least one
aggregator device having at least one optical transceiver to
initiate a series of communications between the embedded smart
plates to determine the location and data collected by each of the
smart plates.
[0012] Additional features of the present invention will become
apparent from the following description and appended claims, taken
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a plan view of a fuel cell system including a fuel
cell stack having a plurality of fuel cells and embedded smart
plates;
[0014] FIG. 2 is a simplified block diagram of one of the embedded
smart plates shown in FIG. 1;
[0015] FIG. 3 is a flow diagram of how an aggregator device
initiates communication and determines the location and data
collected by each of the smart plates shown in FIG. 1; and
[0016] FIG. 4 is a plan view of a fuel cell system having a
plurality of fuel cells, embedded smart plates and two aggregator
devices for collecting location and measurement data for the smart
plates in the stack.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0017] The following discussion of the embodiments of the invention
directed to a system and method for monitoring measured parameters
of each fuel cell or a group of fuel cells in a fuel cell stack
utilizing an aggregator device is merely exemplary in nature, and
is in no way intended to limit the invention or its applications or
uses.
[0018] FIG. 1 is a plan view of a system 10 including a fuel cell
stack 12 having a plurality of fuel cells 14. Although not shown
for the sake of clarity, each fuel cell 14 includes a fuel cell
membrane, an anode side diffusion media layer, and a cathode side
diffusion media layer, as would be readily apparent to those
skilled in the art. Stack plates 20 are also part of the system 10,
such as a bipolar plate between each fuel cell 14 and a unipolar
plate on each end of the stack 12, where the side of the stack
plate 20 facing the anode side diffusion media layer includes anode
side reactant gas flow channels (not shown) and the side of the
stack plate 20 facing an adjacent fuel cell 14 includes cathode
reactant gas flow channels (not shown). Additionally, the stack
plates 20 include cooling fluid flow channels (not shown).
[0019] In a fuel cell stack that is measured in series by virtue of
the topology and geometry of the fuel cells in the stack, it is
desirable to measure certain parameters for the purpose of
controlling the operation of the stack. Such parameters may include
the voltage potential across individual cells or groups of cells,
the temperature at certain points within the stack, or any other
quantifiable parameter which may be represented by an electrical
signal or numeric value, such as high frequency resistance
(HFR).
[0020] According to the present invention, a measurement value such
as the voltage or HFR of each fuel cell 14, or group of fuel cells
14, is measured by an embedded smart plate (ESP) 30. Each ESP 30
includes an ESP printed circuit board 32, described in detail
below, and at least one connector 28 for connecting the ESP printed
circuit board 32 to one of the stack plates 20. Thus, the ESPs 30
are arranged in the stack analogous to, and possibly embedded
within, the stack 12 in a columnar arrangement such that each ESP
printed circuit board 32 in the stack 12 is located immediately
above or below each printed circuit board 32 adjacent to it.
[0021] When the ESPs 30 are embedded, and/or powered by the cells
14 of the stack 12, communicating with the ESPs 30 while
maintaining electrical isolation between the ESPs 30 and a control
device, such as an aggregator device 40 (discussed below), is
necessary because operation of the fuel cell stack 12 may create a
large common mode voltage potential between the stack 12 and the
aggregator device 40. To maintain the necessary electrical
isolation, the present invention utilizes the aggregator device 40.
The ESP 30 adjacent to the aggregator device 40 is the starting
point for communication. The aggregator device 40 is placed at some
location within the fuel cell stack 12, typically at one end, to
request and coordinate the location and measured values of each
fuel cell 14, or a group of fuel cells 14, in the stack 12.
[0022] Each ESP 30 is mechanically and electrically connected to at
least one of the stack plates 20, thereby allowing the ESP printed
circuit board 32 to receive parasitic operating power from, and
measure various measured values, such as the voltage of the fuel
cell 14, or group of fuel cells 14, corresponding to the stack
plate 20 that the printed circuit board 32 is connected to. The
system 10 illustrates an ESP 30 connected to every other stack
plate 20 in the fuel cell stack 12, thereby requiring each ESP 30
to measure the voltage, for example, of two fuel cells 14 in the
stack 12. In an alternate embodiment, each ESP 30 may be
electrically coupled to five consecutive stack plates 20 using
various interconnection devices, thereby allowing the measured
value of four fuel cells 14 to be determined by a single ESP 30.
Each of the ESP printed circuit boards 32 also includes optical
transceivers 34 mounted on the geometric top surface and the bottom
surface of the circuit board 32. The optical transceivers 34 are
utilized for sending and receiving information via modulated
signals that may be conveyed between the ESPs 30, as is described
in detail below.
[0023] The aggregator device 40, which is a variation of the ESP
printed circuit board 32, receives its operating power from a
battery 42 instead of from a fuel cell 14, thereby maintaining
galvanic isolation between the ESPs 30 and the aggregator device 40
without requiring the use of costly electrical isolation
components. The aggregator device 40 initiates communication with
the first ESP 30 in the fuel cell stack 12 using the optical
transceivers 34 located on the aggregator device 40 to establish
the location of the first ESP 30 in the stack 12, and collect, for
example, the minimum measured voltage of the fuel cell 14, or group
of fuel cells 14, associated with the stack plate(s) 20 to which
the first ESP 30 is connected. Each ESP 30 in the stack 12 is
communicated with to determine the location and the minimum cell
voltage of each fuel cell 14 in the stack 12 in a daisy-chain
fashion, i.e., in series, using, for example, a 9/N/1 protocol,
until the location and the minimum cell voltage of all the fuel
cells 12 in the stack 10 are known. Other measurements of the fuel
cells 14 may be performed as well, for example, measured HFR of
each fuel cell 14. In this way, the ESP 30, in conjunction with the
aggregator device 40, communicates the location and measurement
information of each fuel cell 14 in the stack 12 to the aggregator
device 40, which may then communicate the location and measurement
information to a control system 44.
[0024] FIG. 2 is a simplified block diagram of the ESP 30,
including a plurality of electronic components that are bonded to
form the ESP printed circuit board 32. Each circuit board 32
includes a low-input-voltage DC-to-DC converter 52 that converts a
small amount of power from the fuel cell 14, or group of fuel cells
14, into a stable and usable operating voltage for the ESP printed
circuit board 32. The circuit board 32 also includes an
analog-to-digital converter 54 that converts the differential
voltage value of the fuel cell 14, or group of fuel cells 14,
(hereinafter, the "measured value") into a numerical value which
may be processed and communicated by a microprocessor 56 that is
electrically coupled to the optical transceivers 34, thereby
enabling communication to adjacent ESPs 30 and/or the aggregator
device 40. The microprocessor 56 may also determine which of the
cells has the minimum cell voltage or the maximum cell voltage, and
other ancillary data (such as its own operational status), which
may also be communicated via the optical transceivers 34. Further,
the ESP printed circuit board 32 includes a voltage reference 58
that generates a stable voltage such that the stable voltage
generated may be compared to the measured value by the
analog-to-digital converter 54. In a non-limiting embodiment of the
present invention, the voltage reference 58 and the
analog-to-digital converter 54 may be integrated into the
microprocessor 56.
[0025] As shown in FIG. 2, each of the ESP printed circuit boards
32 has two of the connectors 28 for connecting the circuit board 32
to the stack plate 20. However, those skilled in the art will
recognize that a variety of designs for connecting the circuit
board 32 to the stack plate 20 may be used without departing from
the scope of the present invention.
[0026] As mentioned above, each ESP printed circuit board 32 also
includes optical transceivers 34 on the top and the bottom of the
circuit board 32 to enable data communication to and from adjacent
ESPs 30 and the aggregator device 40. The aggregator device 40 also
includes optical transceivers 34 for communicating with the ESPs
30. Each of the optical transceivers 34 includes an optical
transmitter 36, such as light emitting diodes (LEDs), and an
optical receiver 38, such as semiconductor light detectors,
photo-transistors, or photodiodes, for sending and receiving
information. The optical transceivers 34 of each ESP printed
circuit board 32 and each aggregator device 40 are aligned for
optical signal communication. More specifically, the optical
transmitter 36 of a first ESP printed circuit board 32 is aligned
with the optical receiver 38 of a second ESP printed circuit board
32, and vice versa, such that the first and second ESP printed
circuit boards 32 are able to send optical information back and
forth, as shown in FIG. 1.
[0027] The optical transmitters 36 and the optical receivers 38 are
selected such that their respective spectral emissivity and
sensitivity are matched and located such that the optical
transmitter 36 on the top side of a central ESP 30 shines directly
onto the photosensitive area of the optical receiver 38 of the next
higher ESP 30 in the stack immediately above the central ESP 30.
Inversely, the orientation of the bottom optical transmitter 36 on
the central ESP 30 shines directly on the optical receiver 38 on
the top side of the next lower ESP 30 in the stack immediately
below the central ESP 30. Data exchanged across LED/detectors of
the optical transceivers 34 by the respective microprocessors of
the sending and receiving ESPs 30, as described above, are
organized into packets of data bits, wherein each data bit is
represented by a pulse of light, and the separation of pulses
determines the value of the data bit. This communication method can
be pulse position modulation (PPM), as is readily apparent to those
skilled in the art. All of the transceivers 34 of the ESP printed
circuit boards 32 are aligned to allow for communication, as the
ESPs 30 in the stack 12 are aligned in a columnar arrangement as
discussed above.
[0028] Many techniques exist in the art where the optical signal
from the optical transceivers 34 can provide an indication of
measured values such as voltage potential, HFR or other ancilliary
data (e.g., the operational status of the circuit board 32). For
example, in an analog version, the intensity of the light from the
optical transmitter 36 can be an indication of the voltage
potential, where the optical signal is proportional to the voltage.
As discussed above, the circuit board 32 may include a voltage
regulator, such as the DC/DC converter 52, to convert the voltage
to a level usable by the optical transceivers 34. Also, the ESP
printed circuit board 32 may include the analog-to-digital
converter 54, discussed above, to generate a digital optical signal
that is frequency modulated to encode the measured values.
[0029] Most optical transceivers, such as LEDs, have a minimum
forward voltage of about 1.2 volts, rendering them impractical for
measuring a single cell voltage. Thus, the ESP printed circuit
board 32 may also include a miniature booster converter to amplify
the measured voltage. The feedback loop of the booster converter
could be designed to have its output current follow the input
voltage, allowing the intensity of the optical transceivers 34 to
vary with the measured values.
[0030] FIG. 3 is a flow diagram 60 illustrating how the system 10
may measure and communicate the cell voltage of each of the fuel
cells 14, or group of the fuel cells 14 in the stack 12. Upon
activation, the aggregator device 40 initiates a protocol to the
first ESP 30 in the stack 12 at box 62. The aggregator device 40
determines the z-axis sequential position of the first ESP 30 by
communicating via the optical transceivers 34 on the aggregator
device 40 and the ESP printed circuit board 32 of the first ESP 30,
which are aligned such that the signals from the optical
transmitter 36 of the aggregator device 40 are directly
communicated to the optical receiver 38 of the optical transceiver
34 of the first ESP 30. Each ESP 30 then communicates with the next
ESP 30 in the columnar arrangement in a daisy-chain fashion, i.e.,
by communicating through each of the ESPs 30 in series by utilizing
the optical transceivers 34 that are located on the top and bottom
of each of the ESP printed circuit boards 32 of the ESPs 30 in the
stack 12 at box 64. The optical transceivers 34 of each of the ESPs
30 are aligned in a columnar arrangement to send and receive
information to each adjacent ESP 30 using the optical transceivers
34 as described above. Thus, the z-axis sequential position of each
ESP 30 in the fuel cell stack 12 may be determined. Subsequently,
the z-axis sequential position of each ESP 30 in the stack 12 is
used to address each ESP 30 and to identify the measured value of
each ESP 30 that is communicated from each of the ESPs 30 using the
optical transceivers 34 at box 66.
[0031] For example, during normal operation, each ESP 30 may
continuously measure the voltage generated by the fuel cell 14, and
more specifically the voltage generated by the fuel cell membrane
that is present across the stack plates 20. When the aggregator
device 40 sends a request for measured voltage to the ESPs 30 at
box 68 via the optical transceivers 34, the ESPs 30 communicate the
measured voltage using digital signaling via the optical
transceivers 34 at box 70. In this way, the ESPs 30 and their
optical transceivers 34 form a bussed data transmission system.
[0032] In an alternate embodiment of the present invention, the
ESPs 30 may employ a true multipoint optical bus to improve
reliability, such as by employing a construction using light-pipe
technology. Thus, the failure of a single ESP 30 would not
interrupt the transmission of measured values and other data to and
from the ESPs 30 located at z-axis sequential positions distal to
the control system 44.
[0033] FIG. 4 is a block diagram of a system 80 similar to the
system 10, where like elements are identified by the same reference
numbers. The system 80 includes two aggregator devices 40 that are
fitted with complimentary optical transceivers 34 to match the
optical transceivers 34 of the topmost and bottommost ESPs 30 that
are exposed at the ends of the stack of the ESPs 30. The aggregator
devices 40 are additionally fitted with a microprocessor 56, which
is electrically coupled to the optical transceivers 34, and which
may be electrically coupled to an external control system such as
the control system 44. The microprocessors 56 of the aggregator
devices 40 at each end of the stack of ESPs 30 are electrically
coupled on a line 86 such that one aggregator acts as a
communications "master" and the other acts as a communications
"subordinate," as is discussed in detail below.
[0034] As discussed above, the aggregator devices 40 are placed at
each end of the stack 12 such that communication of the measured
values may be requested and coordinated. A request may come from
radio frequency (RF) or radio frequency identification (RFID) type
communications from an external device such as the control system
44. Additionally, capacitive coupling could be used to communicate
digital data between adjacent ESPs 30, thus providing galvanic
isolation by blocking DC voltage and passing AC voltage.
[0035] As discussed above, in the non-limiting embodiment of FIG.
4, the system 80 may be fitted with the aggregator devices 40 at
the top and the bottom of the stack 12. One of the aggregator
devices 40 acts as a "master" aggregator 82 and the other
aggregator device 40 acts as a "subordinate" aggregator 84. The
master aggregator 82 begins communication by issuing a command (in
the form of a pulse-position modulation (PPM) packet) to the ESP 30
adjacent to the master aggregator 82 via the optical transmitter 34
on the bottom side of the master aggregator 82. The ESP 30 adjacent
to the master aggregator 82 receives the communication via the
optical receiver 34 located on the top side of the ESP 30. The ESP
30 adjacent to the master aggregator 82 then executes the command
issued from the master aggregator 82, which might include capturing
a measurement value or substituting measurement data into the PPM
packet's data payload.
[0036] Following execution of the command from the master
aggregator 82 by the adjacent ESP 30, the ESP 30 adjacent to the
master aggregator 82, i.e., the first ESP 30, attempts to issue the
command (possibly with modified payload) to the next ESP 30 in the
columnar arrangement, i.e., the second ESP 30. Thus, the topmost
ESP 30 executes the command issued from the master aggregator 82,
which might include capturing a measurement value or substituting
measurement data into the PPM packet's data payload. Following
execution of the command, the topmost ESP 30 attempts to issue the
command (possibly with modified payload) to the next ESP 30, moving
longitudinally "away" from the ESP 30 along the stack of ESPs. This
process of communication continues to each ESP 30 in the stack 12
until the cycle of command-issue, command-acknowledgment and
command-execution is repeated by all the ESPs 30 in the stack
12.
[0037] The system 80 utilizes ESPs 30 on every other stack plate
20, therefore, each ESP 30 in the system 80 measures a group of two
fuel cells 14 in the stack 12. For example, the master aggregator
82 communicates its voltage, and the first ESP 30 measures the
total voltage and subtracts the voltage of the master aggregator 82
to determine the measured voltage value of the group of cells 14
associated with the first ESP 30. The first ESP 30 may then
communicate the total value and its value, and the second ESP 30
may subtract the total value communicated by the first ESP 30 to
determine the measured voltage value of the group of cells 14
associated with the second ESP 30. If a minimum voltage request was
sent by the control system 44, the second ESP 30 will determine if
the measured voltage of the second ESP 30 is less than the measured
voltage of the first ESP 30. If so, the second ESP 30 communicates
the total measured value including the measured value of the group
of fuel cells 14 associated with the second ESP 30, and the value
of the measured voltage of the group of cells 14 associated with
the second ESP 30 as the minimum voltage value recorded thus far in
the stack 12 to a third ESP 30 in the stack 12. Each ESP 30 repeats
the process as described above with respect to the second ESP 30
until all the voltage values of the groups of the fuel cells 14 are
known, and the group of fuel cells 14 with the minimum voltage has
been identified.
[0038] After the bottom-most ESP 30 in the stack 12 executes the
command, it issues the command (possibly with modified payload) to
the subordinate aggregator 84. The subordinate aggregator 84
receives the command, and transmits a success message to the master
aggregator 82 via the electrical coupling on the line 86.
[0039] While the above non-limiting embodiment utilizes the master
aggregator 82 at the top of the stack 12 and the subordinate
aggregator 84 at the bottom of the stack 12, the location of the
master aggregator 82 and the subordinate aggregator 84 may be
located interchangeably at either end of the stack 12.
[0040] According to the non-limiting embodiment described in FIG. 4
that includes the master aggregator 82 and the subordinate
aggregator 84, a failed or inoperative ESP 30 that interrupts the
flow of the command-issue, command-acknowledgment and
command-execution cycle may be overcome. For example, if an ESP 30
has failed or is inoperative, that ESP 30 will not acknowledge the
command that has been issued by the master aggregator 82 or the ESP
30 adjacent to the failed ESP 30, if applicable. If this occurs,
and the command issuer is an ESP 30 in the stack 12, the ESP 30
issuing the command to the failed ESP 30 may reverse the direction
of communication by issuing the command (or a modified command to
indicate the failure) to the ESP 30 from which the command was
originally received.
[0041] The reversal of the direction of communication of the ESPs
30 allows the command, or modified command, to be relayed back to
the aggregator device 40 that originated the command, thereby
allowing detection of the failure.
[0042] In the case that the master aggregator 82 originated the
command, and a communication failure is detected, the master
aggregator 82 may transmit a message using the line 86 to request
that the subordinate aggregator 84 issue the command to the ESP 30
adjacent to the subordinate aggregator 84 at the opposite end of
the stack 12, thereby allowing the stack 12 to be interrogated from
both ends. In this way, the system 80 may prevent the loss of
measurement data from a portion of the stack 12 due to a single
failed or inoperative ESP 30.
[0043] In another non-limiting embodiment, an additional pair of
optical transceivers 34 may be installed on the top and bottom
surfaces of each ESP 30 in the stack 12. Each ESP 30 is also fitted
with apertures in alternating geometric locations such that PPM
packets may be directed "around" a failed or inoperative ESP 30. In
this way, the loss of measurement data from a portion of the stack
12 due to the presence of two failed or inoperative ESPs 30 in the
stack 12 may be prevented, provided that the failed or inoperative
ESPs 30 are not immediately adjacent to each other in the stack
12.
[0044] In another non-limiting embodiment, the optical transmitters
36 and the optical receivers 38 of the optical transceivers 34 on
each of the ESPs 30 may have different spectral emissions and
responses, respectively, and may be employed for "upward-bound" and
"downward-bound" PPM packets. In this way, the cross-talk between
the optical transceivers 34 located on the ESPs 30 that are in
close physical proximity to one another in the stack 12 may be
minimized or eliminated.
[0045] The foregoing discussion discloses and describes merely
exemplary embodiments of the present invention. One skilled in the
art will readily recognize from such discussion and from the
accompanying drawings and claims that various changes,
modifications and variations can be made therein without departing
from the spirit and scope of the invention as defined in the
following claims.
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